Kaganowicz, in U.S. Pat. No. 4,328,646, describes a method for preparing a silicon oxide (SiO.sub.x) coating on a substrate which includes subjecting silane and a gaseous, oxygen-containing compound selected from the group consisting of N.sub.2 O, H.sub.2 O and CO.sub.2 to a glow discharge. Kaganowicz et al, in U.S. Pat. No. 4,355,052 entitled "Method for Obtaining an Abrasive Coating", disclose a method in which subjecting SiH.sub.4 and N.sub.2 O to a glow discharge for the purpose of depositing SiO.sub.x onto a substrate includes the additional step of adjusting the refractive index and thickness of the SiO.sub.x coating by means of the glow discharge deposition process parameters so as to maximize the micromachining efficiency of the SiO.sub.x coating.
The resulting silicon oxide coatings can effectively lap hard materials such as diamone. One application of the silicon oxide coatings is in the shaping of a diamond playback stylus for use with capacitive information disc records. A method for producing suitable styli was described in Keizer in U.S. Pat. No. 4,104,832. An improved coating capable of decreasing the micromachining time to lap such styli would be useful for high volume production.